Control interface, system and method

ABSTRACT

A pilot control interface and method are described for selective control of an autopilot system by a pilot of an aircraft in which the autopilot system is installed. The pilot control interface includes a passive network that is selectively switchable between a plurality of states across an output interface that is made up of no more than two conductors that are in electrical communication with the autopilot system. Modification of a current autopilot flight mode can be performed incrementally or continuously based on respective momentary and continuous pilot input actuations.

RELATED APPLICATION

This application is a continuation application of copending U.S. patentapplication Ser. No. 15/231,650 filed on Aug. 8, 2016; which is acontinuation application of U.S. patent application Ser. No. 14/133,601filed on Dec. 18, 2013 and issued as U.S. Pat. No. 9,415,862 on Aug. 18,2016; the disclosures of which are incorporated herein by reference intheir entirety.

BACKGROUND

The present application is generally related to a control system and,more particularly, to a control interface for a control system andassociated methods. Further, a method and associated apparatus formanaging rotorcraft flight are described.

Control systems can generally be subject to stringent requirements, forexample, with respect to reliability. Using the framework of an aircraftautopilot by way of example, it is necessary that the autopilot does notproduce any operational condition of the helicopter or other aircraftthat could present an operational risk or induce an emergency condition.Such reliability considerations also apply to a pilot control interfacethat is provided for purposes of allowing the pilot to control theautopilot. For instance, the possibility of an unintentionaldisengagement of the autopilot should be avoided. The pilot controlinterface often utilizes a plurality of electrical switches that areaccessible to the pilot for controlling the various functions of theautopilot such as flight control mode and engagement/disengagement. Ofcourse, it is necessary to electrically interface these switches to thecontrol unit of the autopilot. In terms of reliability of thiselectrical interface, it is submitted that the perception of the priorart centers on an electrical architecture that utilizes individualelectrical conductors connected to each switch and extending from eachswitch to the autopilot or central control unit. Applicants recognize,in this regard, that there can be limitations involved when thisarchitecture is employed, as will be further discussed below.

The foregoing examples of the related art and limitations relatedtherewith are intended to be illustrative and not exclusive. Otherlimitations of the related art will become apparent to those of skill inthe art upon a reading of the specification and a study of the drawings.

SUMMARY

The following embodiments and aspects thereof are described andillustrated in conjunction with systems, tools and methods which aremeant to be exemplary and illustrative, not limiting in scope. Invarious embodiments, one or more of the above-described problems havebeen reduced or eliminated, while other embodiments are directed toother improvements.

In one aspect of the disclosure, a pilot control interface andassociated method are described for selective control of an autopilotsystem by a pilot of an aircraft in which the autopilot system isinstalled. The pilot control interface includes an electrical resistancenetwork that is selectively switchable between a plurality of states. Aplurality of switches is arranged for pilot interaction therewith toselectively switch the electrical resistance network between the statessuch that each state exhibits an output resistance across an outputinterface that is made up of no more than two conductors that are inelectrical communication with the autopilot system.

In another aspect of the disclosure, a pilot control interface andassociated method are described for selective control of an autopilotsystem by a pilot of an aircraft in which the autopilot system isinstalled. The pilot control interface includes a network of passiveelectrical components that is selectively switchable between a pluralityof states responsive to pilot interaction with a plurality of switchessuch that each state exhibits an output characteristic across an outputinterface that is made up of no more than two conductors.

In still another aspect of the disclosure, an autopilot system andassociated method are described for selective control of an aircraft.Accordingly, one or more actuators control communication with one ormore flight controls of the aircraft. An autopilot controller is inelectrical communication with the actuators and configured for automaticcontrol of the aircraft in one or more flight modes and a pilot controlinterface includes (i) an electrical resistance network that isselectively switchable between a plurality of states and (ii) aplurality of switches for pilot interaction therewith to selectivelyswitch the electrical resistance network between the states such thateach state exhibits an output resistance across an output interface thatis made up of no more than two conductors that are in electricalcommunication with the autopilot controller.

In a further aspect of the disclosure, an autopilot system andassociated method are described for controlling the flight of ahelicopter having a control stick that is operable by the pilot tomanually control the flight of the helicopter. Accordingly, an inputarrangement is located on the control stick including a left switch, aright switch, a fore switch and an aft switch. An actuator arrangementreceives a set of control signals to control the flight of thehelicopter in a current flight mode of the autopilot and a processingsection monitors the flight of the helicopter to generate the set ofcontrol signals responsive to the monitoring and to respond to a pilotactuation of one of the switches by changing a flight parameter of thehelicopter relating to the current flight mode.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are illustrated in referenced figures of thedrawings. It is intended that the embodiments and figures disclosedherein are to be illustrative rather than limiting.

FIG. 1 is a hybrid view, partially in perspective and partially in theform of a block diagram, illustrating an embodiment of an autopilotsystem, including an embodiment of a pilot control interface inaccordance with the present disclosure.

FIG. 2 is a schematic diagram illustrating details of an embodiment ofthe pilot control interface of FIG. 1 as well as its interface to anautopilot control unit of the autopilot system which is shown in blockdiagram form.

FIG. 3 is a diagrammatic partially exploded view, generally from a frontperspective, of an embodiment of the autopilot control interface, shownhere to illustrate details of its structure.

FIG. 4 is another partially exploded view, generally from a rearperspective, of the embodiment of the autopilot control interface ofFIG. 3, shown here to illustrate further details of its structure.

FIG. 5 is an assembled view, taken generally from a rear perspective, ofthe autopilot control interface of FIGS. 3 and 4, showing additionaldetails of its structure.

FIG. 6 is a flow diagram illustrating an embodiment for a method ofoperation of the autopilot system in cooperation with the pilot controlinterface of the present disclosure.

FIG. 7 is a diagrammatic view, in perspective, illustrating anotherembodiment of the pilot control interface of the present disclosure.

FIG. 8 is a schematic diagram illustrating details of another embodimentof the pilot control interface of FIG. 1 as well as its interface to theautopilot control unit of the autopilot system which is shown in blockdiagram form.

FIG. 9 is a flow diagram illustrating an embodiment of a method formanaging rotorcraft flight in accordance with the present disclosure.

FIG. 10 is a screen shot illustrating an embodiment of the appearance ofa display in an autorecovery mode.

FIGS. 11 and 12 are screenshots illustrating the appearance of a displayin a speed hold flight mode of the autopilot for purposes of changingtrack angle and/or speed.

FIGS. 13 and 14 are screenshots illustrating the appearance of a displayin an altitude flight mode of the autopilot for purposes of changingtrack angle and/or altitude.

DETAILED DESCRIPTION

The following description is presented to enable one of ordinary skillin the art to make and use the invention and is provided in the contextof a patent application and its requirements. Various modifications tothe described embodiments will be readily apparent to those skilled inthe art and the generic principles taught herein may be applied to otherembodiments. Thus, the present invention is not intended to be limitedto the embodiment shown, but is to be accorded the widest scopeconsistent with the principles and features described herein includingmodifications and equivalents. It is noted that the drawings may not beto scale and may be diagrammatic in nature in a way that is thought tobest illustrate features of interest. Descriptive terminology may beadopted for purposes of enhancing the reader's understanding, withrespect to the various views provided in the figures, and is in no wayintended as being limiting.

FIG. 1 is a diagrammatic view illustrating an embodiment of an autopilotsystem, generally indicated by the reference number 10. The autopilotsystem includes an embodiment of a pilot control interface 12 that canbe mounted to a cyclic control or stick 16 of a helicopter. In thepresent example, the helicopter is a Robinson R22, although the pilotcontrol interface and autopilot system can be used with any suitableaircraft and is not limited to helicopters. It is noted that the cycliccontrol is partially illustrated. As will be appreciated by one ofordinary skill in the art, stick 14 can be moved fore and aft (towardand away from an instrument console) to control pitch of the helicopterand transversely for purposes of controlling roll of the helicopter in acoordinated manner to produce controlled flight. Additional controlinputs are provided by the pilot via a pair of pedals in order tocontrol the yaw orientation of the helicopter by changing the pitch of atail rotor. It is noted that these latter helicopter components have notbeen shown for purposes of illustrative clarity but are understood to bepresent. In an embodiment, the pilot also remains in control of thecollective of the helicopter as well as the throttle settings. Theautopilot of the present disclosure, however, can exert full controlauthority over stick 16 by moving the stick in any direction to thelimits of its travel under appropriate circumstances. Stick 16 passesbelow a deck of the helicopter and engages pitch and roll linkages andactuators of the autopilot so as to control cyclic actuation of the mainrotor of the helicopter. The term “cyclic” refers to the variation inpitch of the rotor blades of the helicopter on a per revolution basis.In this regard, cyclic control can refer to manipulation of the stick orthe stick itself can be referred to as the cyclic. It should beappreciated that the teachings that have been brought to light hereinremain applicable in the context of an autopilot that additionallycontrols one or more of throttle, collective and yaw.

In the Robinson R22, what can be referred to as a teetering orT-configured cyclic control or stick is used, however, the pilot controlinterface and autopilot system of the present disclosure can be used inconjunction with any configuration of aircraft control stick, eithercurrently available or yet to be developed. While supporting the pilotcontrol interface on the stick provides for convenient access by thepilot as well as benefits yet to be described, the pilot controlinterface can be panel mounted. Moreover, the concepts that are broughtto light herein are submitted to be equally applicable in other fieldsof endeavor and are not limited to aircraft, suitable examples includebut are not limited to video games, remote crane operation, fixed wingaircraft, military and commercial vehicles, boats, hovercraft and acomputer cursor.

A housing 30 forms part of the pilot control interface and includes aplurality of buttons that interface with corresponding switches that aresupported internal to the housing. The housing can be formed, forexample, from a suitable plastic and/or metal using molding and/ormachining. For purposes of convenience, each button and its associatedswitch may be referred to as a switch. Switches 24 and 26 are originalequipment on the R22 and have been relocated to housing 30 which isitself mounted to cyclic control 16. Switches 24 and 26 allow the pilotto selectively change frequencies on a factory installed nav-com unit(not shown). Switch 24 changes the communications frequency while switch26 changes the navigational frequency. Such a radio unit allows thepilot to program a new frequency into a stand-by channel for nav andcom. By pressing the appropriate switch, the active and stand-byfrequencies are interchanged. The pilot can then choose to reprogram thestand-by frequency or save the old frequency if he/she chooses to returnto it. The pilot control interface is in electrical communication withan autopilot control unit 34 via an electrical interface 36. The set offlight modes that is available in the autopilot can include but is notlimited to speed hold, altitude hold, hover, position hold and GPSProgram. The autopilot control unit is itself in electricalcommunication at least with a pitch actuator 38 a and a roll actuator 38b. The actuators can be housed below deck in the helicopter andinterfaced to a lower end of the stick via suitable linkages. Theautopilot control unit is interfaced with a display 40 that can beprovided at any appropriate location that is visible to the pilot. Thefunction of an autopilot control unit in association with actuators thatare mechanically coupled to aircraft controls is well known. In thepresent example, a parallel control system is provided which leaves theoriginal cyclic control linkages of the helicopter intact. A series typeautopilot control system, in contrast, requires breaking the originalcyclic control linkages of the helicopter between the stick and rotorsuch that the autopilot actuators can be inserted into the break. Itshould be appreciated that the teachings herein can readily be appliedto a series control input embodiment. It is noted that an advancedautopilot control unit and associated actuators are described, forexample, in U.S. patent application Ser. Nos. 13/763,574, 13/763,582 and13/763,590 each of which is commonly owned with the present applicationand all of which are hereby incorporated by reference. The pilot controlinterface further includes a left switch SW1, a right switch SW2, a foreswitch SW3 and an aft switch SW4 that are arranged in an intuitivemanner on the face of the pilot control interface. Generally, eachswitch can include a normally open contact. In the present embodiment, amode select switch SW5 serves as a selection switch and at least allowsthe pilot to switch between and control the flight modes of theautopilot. In another embodiment, what can be referred to as a top hatswitch can be used to replace switches SW1-SW5, as will be described atan appropriate point hereinafter.

An engage/disengage selector 50 at least provides for highly reliableengagement and disengagement of the autopilot system by the pilot. Inthe present embodiment, the button associated with the engage/disengageselector can be received within a recess 54 on the face of the pilotcontrol interface to protect from inadvertent actuations and to providefor tactile distinction of this important function. It is well-knownthat an inadvertent disengagement, in particular, of an autopilot mightproduce flight conditions that require the immediate attention of thepilot. Of course, any disengagement of the autopilot can be accompaniedby aural, haptic and/or visual caution indications. As will be furtherdescribed, pilot control interface 12 and engage/disengage selector 50,in particular, are configured to ensure a high degree of reliability interms of electronic interpretation of the output state of the pilotcontrol interface, for example, to provide enhanced noise immunity aswell as reliable detection of potential failure modes.

Attention is now directed to FIG. 2 in conjunction with FIG. 1. Theformer is a schematic diagram illustrating autopilot system 10 includingan embodiment of pilot control interface 12. Switches SW1-SW5 areillustrated as part of a parallel resistance network 52 that iselectrically connected across electrical interface 36. In particular,each switch is placed in series with one of resistors R1-R5,respectively, to form branches of the parallel resistance network. Inthe present embodiment, R1 is 2.2 KΩ, R2 is 3.1 KΩ, R3 is 4.7 KΩ, R4 is8.5 KΩ and R5 is 18 KΩ. Of course, a tolerance is associated with eachof these values. Any resistors used herein can be selected with anappropriate tolerance as well as other appropriate characteristicsincluding, for example, thermal stability. Thus, R1-R5 with respectiveswitches SW1-SW5 form five parallel branches. Another parallel branchincludes resistor R6 which may be referred to as a null resistor. In thepresent embodiment, R6 has been selected as 75 KΩ. It is noted that, inthe present embodiment, R6 serves as the highest branch resistancevalue. Engage/disengage selector 50 is illustrated within a dashedrectangle. In an embodiment, the engage/disengage selector can comprisetwo parallel branches of the parallel resistance network wherein a firstbranch is made up of a switch SW6 and a resistor R7 and a second branchis made up of a switch SW7 and a resistor R8. Resistors R7 and R8 are ofequal values in the present example, although this is not required, andcan comprise the lowest resistance of any branch of the parallelnetwork. As will be described in detail below, switches SW6 and SW7 arearranged such that a pilot actuation of the engage/disengage selector isintended to produce a simultaneous closure of switches SW6 and SW7 forpurposes of redundancy and/or enhanced reliability. Thus, actuation ofthe engage/disengage selector normally produces a resistancecontribution to the network that is equal to the parallel combination ofR7 and R8. It is noted that any suitable type of switch or combinationof switches can be utilized as SW1-SW7. One suitable switch is thereadily available TL6200 series switch having a lifetime actuationrating of 10 million cycles, as well as allowing for the independentselection of actuator buttons having differing lengths. The actuatorbutton includes a post that is received by the switch body using a snapfit. Details with respect to the selection of appropriate resistancevalues and operation of the circuitry will be provided at appropriatepoints hereinafter.

Referring to FIG. 2, electrical interface 36 is made up of twoconductors 36 a and 36 b that are connected across the parallel networkat terminations T1 and T2, and extend to autopilot control unit 34. Itshould be appreciated that only two electrical conductors are needed tomake up interface 36, aside from shielding considerations. For enhancedimmunity, one or both of the conductors can include a shield 54. Inanother embodiment, a twisted shielded pair can be used as interface 36.The latter can be grounded at the pilot control interface end and/or atthe autopilot control unit end. In still another embodiment, a shieldedcoaxial cable can be used wherein the shield serves as one conductorconnected to T2 and the central conductor serves as a signal leadconnected to T1. In the present embodiment, the autopilot control unitdrives interface 36 using a constant current source 60. Ananalog-to-digital (A/D) converter 64 is electrically connected acrossthe sense resistor. An output 68 of the analog to digital converter isprovided to a processor 70 for purposes of monitoring pilot actuationsas well as monitoring the status of pilot control interface 12. Inanother embodiment, a constant voltage source can be used in series witha sense resistor R_(s) to drive pilot control interface 12. In thiscase, A/D 64 can monitor the voltage across the sense resistor. Thevalue of the sense resistor can be selected, for example, based on theminimum current that is reliably detectable by the A/D converter. Inthis regard, any suitable drive/monitoring arrangement can be employedin cooperation with the pilot control interface including constantcurrent drive and/or constant voltage drive.

Having described pilot control interface 12 and associated monitoringarrangements in detail above, attention is now directed to details ofits operation. Resistors R1-R8 are selected such that potential pilotactuations produce resistances that are unique across an allowed rangeof resistance. In the present embodiment, the allowed range ofresistance is defined by the parallel combination of R7 and R8 of theengage/disengage selector as a lower limit and null resistor R6 as anupper limit. The allowed resistance range in the present example,therefore, is at least approximately 365 Ω to 75 KΩ, accounting fortolerances cabling resistance, connection resistance and the like. Inthis regard, the resistance values that are produced by actuation of anyone of SW1-SW5 as well as actuation of engage/disengage selector 50,whether in normal operation or a partial failure condition, can beunique thereby producing readily distinguishable voltage values acrossanalog-to-digital converter 64. Further, by spacing the allowedresistance states sufficiently apart, essentially the full resolution ofanalog-to-digital converter 64 can be utilized in this embodiment aswell as another embodiment that is yet to be described such that manycounts of the A/D are present between each state of the switchingnetwork. For example, the states can be spaced apart by at least threecounts of the A/D. In this way, noise immunity can be enhanced forpurposes of distinguishing between the allowed states. For example, a 10bit analog-to-digital converter is capable of producing 1024 outputstates or counts. In the resistance network of FIG. 2, using sevenindependent switches, 128 states can at least potentially be produced.It is noted, however, that the number of states is reduced slightly dueto the configuration of the engage/disengage selector havingequal-valued resistors such that a total of 96 states can be produced.Accordingly, more than 10 counts can be present between each outputstate of the switching network for evenly spaced states. As will befurther described, however, the spacing between states can becustomized, for example, based on the criticality or importance of atleast certain ones of the states. It is noted that combination switchactuations can be utilized in a selective manner as allowed statesand/or ignored states. As will be further discussed, the minimumresistance, in the absence of any switch actuation, can be representedby null resistor R6 as an allowed state and an upper limit of theallowed resistance range. Table 1 presents a resistance value that isassociated with a number of allowed states in the present embodiment.

TABLE 1 Allowed State no. Resistance Reference no. Function (Switch) S1365 Ω R7//R8 Engage/Disengage (SW6 and SW7) S2 730 Ω R7 or R8Engage/Disengage (SW6 or SW7) S3 2.2 KΩ R1 Left (SW1) S4 3.1 KΩ R2 Right(SW2) S5 4.7 KΩ R3 Fore (SW3) S6 8.5 KΩ R4 Aft (SW4) S7 18 KΩ R5 Mode(SW5) S8 75 KΩ R6 Open wire detection (null resistor)

Referring to Table 1, it should be appreciated that state S1 representsa normal actuation of the engage/disengage selector while state S2represents a partial failure thereof. In one failure mode, one of SW6 orSW7 fails open. An equivalent failure mode would be an open failure ofone of R7 and R8. In another failure mode, one of SW6 and SW7 failsclosed or shorted. The latter can be identified based on the detectionof a long term presence of the S2 state on interface 36. In oneembodiment, the failure of one of switches SW6 and SW7 in theengage/disengage selector can be regarded as noncritical such that theautopilot remains operational and signals the pilot of the noncriticalfailure. In another embodiment, this failure can be regarded as criticaland the autopilot can notify the pilot to take over control. By way ofnon-limiting example, an open failure mode of one of these switches canbe regarded as a noncritical failure, since this failure mode does notserve to mask other actuation states. As another example, a shortedfailure mode of one of these switches can be regarded as a criticalfailure since such a failure mode can at least partially mask other,higher resistance actuation states. Because the resistance values for R7and R8 in the engage/disengage selector are equal in the presentembodiment, the autopilot system is unable to distinguish whether switchSW6 or SW7 has failed. In another embodiment, R7 and R8 can be ofresistances that are sufficiently different such that the autopilot candistinguish between the failure of SW6 and SW7. In this case, anadditional allowed state can be introduced. By way of non-limitingexample in such an embodiment, R7 can be selected as 700 Ω with R8 beingselected as 800 Ω. States S3-S7 are associated with actuations ofswitches SW1-SW5, respectively. State S3 is spaced apart from state S1by a factor of approximately six in resistance value to provide enhancedreliability and noise immunity with respect to distinguishing state S1from actuations of SW1-SW5. On a state-to-state basis, state S1 can bespaced apart from the nearest allowed state during normal operation by afactor that is greater than the spacing between any other two adjacentstates for enhancement of reliability and noise immunity. It is notedthat the resistance values that are set forth in Table 1 are notintended as being limiting and any suitable set of values can beselected in light of the teachings herein. For example, values can beselected to represent binary combinations based on the series 1, 2, 4,8, 16, 32, etc. In such an embodiment, the resistor values can be 1 KΩ,2 KΩ, 4 KΩ, 8 KΩ, 16 KΩ, 32 KΩ, etc. In this way, multiple switches canbe actuated and the switches can be resolved based on the net binaryvalue. For example, if switches associated with the values 8 KΩ, 2 KΩand 1 KΩ were simultaneously actuated, the detected value would be 11 KΩsuch that the depressed switches are known since only one combination ofswitch actuations corresponds to 11 KΩ. The binary values can berepresented by the current passing through each switch and the sensor,such as, for example an A/D converter can remotely sense the totalcurrent. In an embodiment, the circuit can be composed of resistors inseries so that each switch can short out an associated resistance orreplace an associated resistance with a value of at least approximatelyzero. Such an embodiment can use normally open or normally closedswitches. In any case, the aggregate series resistance identifies theswitches that were depressed.

While not required, by using the actuation of the engage/disengageselector to represent the lowest allowed resistance/state, it should beappreciated that no other actuation is able to mask this value. That is,analog-to-digital converter 64 is able to recognize state S1 even if oneor more of switches S3-S7 is simultaneously actuated or shorted in afailure mode. For example, even if every switch (SW1 through SW5) isclosed in combination with the engage/disengage selector, a resistanceof approximately 255 Ω is produced. In an embodiment, this latterresistance or some other suitable combination of actuation-basedresistances can be used as a lower limit of the allowed resistancerange. Detected voltages that are associated with resistance values thatare lower than the lower limit can be interpreted by CPU 70 as beingindicative of a short in interface 36. Responsive to detection of ashorted condition, an indication can be provided to urge the pilot totake over control of the aircraft, if the autopilot is active.

Turning now to FIG. 3, a partially exploded view, in perspective, ofautopilot control interface 12 is shown for purposes of illustrating thedetails of an embodiment of its internal structure. Housing 30 isconfigured to receive a main printed circuit board 300 which supportsand electrically interfaces switches SW1-SW5 for alignment withcooperating openings that are defined in a faceplate of the housing. Thehousing is also configured to support nav-com switches 24 and 26.Switches SW6 and SW7 of engage/disengage selector 50 are supported andelectrically interfaced by an engage/disengage selector printed circuitboard 304. In an embodiment, board 304 includes a circular periphery,although any suitable shape can be used. Switches S6 and S7 aresupported on opposing sides of board 304 in a back-to-backconfiguration, sandwiching the board therebetween.

Referring to FIG. 4 in conjunction with FIG. 3, the former is a rearview, in perspective, taken from behind autopilot control interface 12.As shown, resistors R1-R8 can be supported and electrically interfacedon a rear surface of main printed circuit board 300. The particularphysical arrangement of these resistors has been provided by way ofexample only, and is not intended as being limiting. For instance, atleast some of the resistors can be located on the opposing, forwardfacing surface of printed circuit board 300. In another embodiment,resistors R6 and R7 can be located on printed circuit board 304 of theengage/disengage selector. A connector 308 can be provided as a terminusof the autopilot control interface, forming one end of electricalinterface 36, as is partially and diagrammatically illustrated forelectrical connection to autopilot control unit 34 or any suitablecomponent.

Attention is now directed to FIGS. 3-5 wherein FIG. 5 is a reardiagrammatic view, in perspective of pilot control interface 12. As seenin FIG. 5, engage/disengage selector 50 can be captured in an installedposition using a bracket 310 that is held in place, for example, usingfasteners 312. The bracket can be formed, for example, by from asuitable plastic and/or metal using machining and/or molding. When sopositioned, a post 328 (FIG. 3), that is supported by bracket 310, canbe received within a central opening 330 (FIG. 4) of the switch body ofSW7 such that post 328 serves as an actuator button for this switch in amanner that is yet to be described. The post can be integrally formedwith the bracket or separately formed, for example, from a suitableplastic or metal and installed on the bracket, for instance, usingthreaded engagement, an interference fit or other suitable expedient. Anopposing, forward end of selector 50 can be captured in position using aperipheral surface 334 of SW7 (FIG. 4) received against an interiorsurface 324 of housing 30 (FIG. 5). It should be appreciated thatengage/disengage selector 50 is received for movement along an actuationdirection 344 within housing 30 responsive to pilot actuations of anengage/disengage button 340 which serves as an actuator for SW6. Thatis, depression of button 308 serves to compress the engage/disengageselector between the button and bracket 310 along actuation direction344 such that SW6 and SW7 are essentially simultaneously closed. Basedupon this floating installation of the engage/disengage selector, a setof flexible conductors 350 extends from main printed circuit board 300to board 304. For purposes of further enhanced reliability, the flexibleconductors can initially be routed through strain relief openings andelectrically connected to contacts 354 (FIG. 3) on an opposite side ofboard 304.

Attention is now directed to FIG. 6 which is a flow diagram thatillustrates an embodiment of a method for the operation of autopilotsystem 10, generally indicated by the reference number 500, inconjunction with pilot control interface 12. The method begins at start504 and proceeds to 508 which can perform a startup self-test.Responsive to the results of the startup self-test, at 512, it isdetermined whether any unresolved errors or anomalies were identifiedprior to the last shutdown of the autopilot system. If any unresolvederrors or anomalies were detected, operation is routed to 516 which canprovide an indication that maintenance is required prior to furtheroperation of the autopilot system. The indication can be provided, forexample, on a display panel of the autopilot system and may beaccompanied by an aural indication and/or illumination of a cautionlight. Operation then ends at 520. If no prior error condition isdetected at 512, operation proceeds to 524 which reads interface 36 in anormal operation mode. At 528 the operational condition of the interfaceis determined. The latter determination can be determined in anysuitable manner. For example, the current operational condition of theinterface can be identified in terms of a detected voltage that can becompared to an allowed voltage range that corresponds to the previouslydescribed allowed resistance range. At 528, the current condition of theinterface is established. For example, it can be determined that theinterface has been compromised based on the detected voltage being outof the allowed voltage range. If the detected voltage is below theallowed voltage range, the interface may be subject to a short circuitfailure. On the other hand, if the detected voltage is higher than theallowed voltage, the interface may be subject to an open circuitfailure. As another example, it can be determined that the interface hasbeen compromised based on a failure of one of switches SW6 and SW7 in amanner that is consistent with the descriptions above. As still anotherexample, a stuck (i.e., shorted) switch can be identified based on ananalysis over time which indicates that a particular switch reads as ifit is in a closed or actuated for an excessive period of time. Thislatter analysis can be applied over a number of iterations through steps524 and 528. At 532, if the condition of the interface is determined tobe compromised, operation is routed to 536 which takes appropriateaction based on the nature of the compromise such as, for example,issuing an indication to the pilot in any appropriate form or form(s).In some embodiments, operation can then be ended at 520, for example,once the pilot takes over control. In other embodiments, the compromisecan be considered as non-critical and normal operation can continue byrouting operation back to step 524, as indicated by a dashed arrow 542.One example of a non-critical error can be regarded as a failure of oneof switches SW6 or SW7 of the engage/disengage selector. If 532determines that pilot control interface operation is normal, the methodbranches to 546 which determines whether the determined conditionrepresents a change in the status of the interface. If not, operation isrouted back to step 524. If the determined condition has changed,operation is routed to 550 which determines the current state of theinterface, for example, based on the states of Table 1. At 554, thestatus of the autopilot is changed based on the determined state. Forexample, the autopilot may be engaged or disengaged. As another example,the flight mode can be changed. As still another example, acharacteristic of a current flight mode can be modified. Operation thenreturns to step 524.

Attention is now directed to FIG. 7 which is a diagrammatic view, inperspective, illustrating another embodiment of the pilot controlinterface of the present disclosure, generally indicated by thereference number 12′. The present embodiment includes a housing 30′which supports a top hat switch 600. The latter includes four switchesthat are arranged in the manner of switches SW1-SW4 of FIG. 4. Each ofthese switches can be individually actuated responsive to appropriatemovements of the top hat as illustrated by double-headed arrows 604.Schematically, interface 12′ can be represented by the schematic of FIG.2 with the exception that mode select switch SW5 may not be needed forthe reason that depressing the top hat at least generally along its axisof symmetry simultaneously actuates all of switches SW1-SW4. Thisactuation can be interpreted as a mode select actuation. By way ofnon-limiting example, the resistance values can be selected based on abinary series, as described above.

Attention is now directed to FIG. 8 which is a schematic diagramillustrating another embodiment of the autopilot system of the presentdisclosure, generally indicated by the reference number 10′. The presentembodiment includes an embodiment 12′ of the pilot control interface. Itis noted that descriptions of like components may not be repeated forpurposes of brevity. Switches SW1′-SW7′ are illustrated as part of aseries resistance network 52′ that is electrically connected acrosselectrical interface 36. It is noted that any suitable type of switchcan be utilized as SW1′-SW7′ such as, for example, the TL6200 seriesswitch. Each switch continues to serve the same function as thecorresponding switch in FIG. 2, however, the switches are normallyclosed and, therefore, open responsive to a pilot actuation. Further,each of switches SW1′-SW5′ is placed in parallel with one of resistorsR1′-R5′, respectively, while switch SW6′ is in parallel with resistorR7′ and switch SW7′ is in parallel with R8′. In the present embodiment,R1′ is 1 KΩ, R2′ is 2 KΩ, R3′ is 4 KΩ, R4′ is 8 KΩ, R5′ is 16 KΩ, R7′ is32 KΩ and R8′ is 64 KΩ. Of course, a tolerance is associated with eachof these values. As noted above, any resistors used herein can beselected with an appropriate tolerance as well as other appropriatecharacteristics including, for example, thermal stability.Engage/disengage selector 50′ is illustrated within a dashed rectangleand, in the present embodiment, includes switches SW6′ and SW7′ alongwith resistors R7′ and R8′. Other than the use of normally closedswitches and modified electrical connections, the mechanicalconfiguration of the engage/disengage selector is unchanged, asillustrated in FIGS. 3-5, such that both switches are actuatedessentially simultaneously responsive to the pilot under normalcircumstances.

In the absence of a pilot actuation during normal operation,engage/disengage selector 50′ presents a resistance of at leastapproximately zero ohms to interface 36. Thus, at least approximatelyzero volts is detectable at interface 36 in the absence of a pilotinteraction. For any switch that is actuated or depressed by the pilot,the value of the associated resistor for that switch is added as acontribution to the resistance value that is presented at interface 36.If multiple switches are actuated, the resistance that is presented atinterface 36 is the sum of the resistor values for the actuatedswitches. For example, switches SW6′ and SW7′ are arranged such that apilot actuation of the engage/disengage selector is intended to producea simultaneous opening of switches SW6′ and SW7′ for purposes ofredundancy and/or enhanced reliability. Thus, actuation of theengage/disengage selector normally produces a resistance contribution tothe network that is equal to the series combination of R7′ and R8′ whichis 96 KΩ in the present embodiment. As another example, a maximumactuation resistance of 127 KΩ corresponds to a simultaneous actuation,however unlikely, of every switch SW1′-SW7′. As the resistance that ispresented at interface 36 increases, the voltage that is detectable atthe interface increases correspondingly since current source I is aconstant current source. In the event of a broken wire condition (i.e.,one or both of wires 36 a and 36 b is broken), the resistance that ispresented at the interface approaches infinity. In this case, thevoltage that is detectable at interface 36 is the maximum voltage thatthe constant current source is capable of delivering. Accordingly,detection of the maximum voltage is indicative of a broken wirecondition. Thus, an actuation of any one of the switches produces aresistance value across the two conductors that falls within a range ofvalid resistance values corresponding to valid states such that detectedresistance values across the two conductors and above the range can beindicative of a broken wire condition. An error or failure condition forengage/disengage selector 50′ is associated with detecting a voltage atinterface 36 that corresponds to the resistance values of R7′ (32 KΩ) orR8′ (64 KΩ). Detection of values indicative of a problem with theengage/disengage selector can be handled in a manner that is consistentwith the descriptions above. Further, detection of any voltage thatcorresponds to a resistance in a range from 96 KΩ (R7′+R8′) to 127 KΩcan be regarded as an engage/disengage selector actuation that isrepresentative of a simultaneous actuation of at least one other switchalong with the engage/disengage selector. In another embodiment, thisrange can extend from 32 KΩ (R7′) to 127 KΩ. Based on the selection ofR7′ and R8′ as high resistance values for the resistance network inconjunction with these latter ranges, masking of an engage/disengageselector actuation due to the inadvertent actuation of one or moreadditional switches is avoided. Detection of a voltage that correspondsto a resistance that is greater than 127 KΩ or a selected higherthreshold value such as, for example, greater than 150 KΩ can beregarded as an open wire condition, resulting in appropriate action suchas, for example, pilot notification. Accordingly, it should beappreciated that embodiment 12′ of the pilot control interface providesbenefits that correspond to those of embodiment 12, as described above.In another embodiment, a constant voltage source can be used in serieswith a sense resistor R_(s) to drive pilot control interface 12′. Inthis case, A/D 64 can monitor the voltage across the sense resistor.

Having described embodiments of the pilot control interface aboveutilizing a switched resistance network, it should be appreciated thatother embodiments can utilize a switched capacitor network, a switchedinductor network, a switched inductor/capacitor (L/C) network or aswitched inductor/capacitor/resistor (LCR) network. These network typescan be driven by an alternating current (a.c.) supply. By way ofnon-limiting example, inductor and/or capacitor a.c. impedances can bespaced apart in essentially the same manners as those associated withresistors. Thus, any suitable arrangement of passive components can beutilized. With this disclosure in hand, it is submitted that one ofordinary skill in the art can readily implement such networks utilizingan alternating current drive. In this regard, it should be appreciatedthat a parallel connection of inductors behaves in an analogous mannerto a parallel connection of resistors (product over sum) while aparallel connection of capacitors behaves in an analogous manner (i.e.,additive) to a series connection of resistors.

Embodiments of the control interface of the present disclosure providebenefits in terms of high reliability, accuracy and noise immunity withrespect to distinguishing the various switched actuation states.Further, selected states such as, for example, a critical state orfunction, as exemplified by the engage/disengage selector describedabove, can be handled in the switched network in a way that provideseven further enhanced reliability and/or accuracy with respect to whatcan be considered as a critical output state or function. Anotherbenefit resides in the need for only two electrical conductors in theinterface leading to the switched network. It should be appreciated, forexample, that separate power leads are not needed. Thus, concerns withrespect to constrained physical space for purposes of routing electricalconnections are reduced to essentially a minimum. It is submitted thatconventional aircraft electrical interconnections typically specify atleast one dedicated electrical conductor for each switch. In some cases,the installation of a cable containing such a required number ofconductors in a pre-existing structure such as, for example, ahelicopter cyclic can be difficult, at the least. As discussed above,the control interface of the present application is not limited to thefield of aircraft controls. In this regard, it is submitted that one ofordinary skill in the art can readily adapt the disclosed controlinterface to a wide range of other fields of endeavor having thisoverall disclosure in hand. It is considered that such adaptation fallswithin the scope of the present application so long as the teachingsthat have been brought to light herein are applied.

Referring to FIG. 9, a method for managing rotorcraft flight isgenerally indicated by the reference number 800. A suitable set offlight modes is described in U.S. Published Patent Application no.2014-0027565 A1, U.S. application Ser. No. 13/763,582, which is commonlyowned with the present application and hereby incorporated by reference.While the method and associated apparatus described herein can be usedwith embodiments of the pilot control interface disclosed herein, itshould be appreciated that this is not a requirement and the teachingsherein can readily be adapted to any suitable interface. The methodbegins at start 802, for example, when the autopilot is activated andproceeds to a self test 806. Certain autopilot modes can beautomatically activated. For example, an attitude recovery mode can beinitiated responsive to engaging the autopilot. This automatic responsecan be based on the attitude at the time of engagement. If thehelicopter is found to be in an unusual attitude at the time ofengagement, the autopilot brings the helicopter to straight and levelflight. An artificial horizon can be displayed in conjunction with theattitude recovery mode, as described above. Accordingly, at 810, theautopilot tests for the presence of an unusual attitude. The parametersfor detection of an unusual attitude can be based, for example, on pitchor roll angle. If an unusual attitude is detected, operation proceeds to814 which initiates an autorecovery mode that restores the helicopter tostraight and level flight. FIG. 10 is a screen shot of display 40illustrating an embodiment of the appearance of the display in theAutorecovery mode. It is noted that each of the flight mode displaysdescribed herein can include a navigation portion having a heading bar820 including a centerline 824 that indicates the current heading of thehelicopter. In an embodiment, the heading bar can be generated based onthe output of a slaved gyro. Below heading bar 820, a track indicator828 and a heading indicator 830 can be provided. Track indicates theangle that the helicopter is moving over the ground and differs from theheading which is the angle the helicopter is pointing, usuallyreferenced to magnetic north. It is noted that the heading can vary withrespect to the course or track indication responsive to crosswinds. Inthe present example, heading bar 820 as well as heading 830 show aheading, HDG, of 298 degrees while track indicator 828 shows a track,TRK, of 295 degrees. For purposes of the autorecovery mode, anautorecovery indication 832 can be provided.

Referring again to FIG. 9, subsequent to autorecovery, normal autopilotoperation can proceed at 918. On the other hand, if an unusual attitudeis not detected at 810, normal operation can thereafter be directlyentered at 918. Generally, the autopilot will enter either a speed holdmode or an altitude hold mode based on the current speed of theaircraft. On the front side of the power curve (above 55 kts, by way ofexample, for an R22), the altitude hold mode is entered, however, atspeeds approaching a maximum speed for the aircraft (102 kts for theR22), the speed hold mode is entered. On the back side of the powercurve (below 55 kts for the R22), the speed hold mode is entered. At922, the pilot control interface is continuously monitored for a pilotactuation of any button/switch. Responsive to an actuation, operationproceeds to 926 which initiates a timer. The time-out value for thetimer can be selected as any suitable value such as, for example,one-half second. Suitable values can be in the range from 0.1 to 1.0seconds. At 930, the autopilot determines whether the actuationinitially detected at 922 remains present following the time-out. If theactuation is no longer present, the actuation is determined to bemomentary and operation proceeds to 934 which performs an incrementaladjustment of the current flight mode of the autopilot and causes anindication to be presented on display 40. For example, in the speed holdmode, a momentary actuation of left switch SW1 or right switch SW2(FIGS. 1 and 2) results in an incremental change in the track angle ofthe aircraft. FIG. 11 is a screenshot of display 40 which illustrates anembodiment of the appearance of the display at the time that theautopilot responds to the actuation. In this example, left SW1 has beenmomentarily actuated, accompanied by the temporary appearance of anarrow 938. The arrow can be displayed, for example, for the duration oftime that is needed by the autopilot to complete the adjustment of thetrack angle. Of course, track indicator 828 and heading 830 will changeresponsive to the track angle adjustment. Such a momentary actuation canresult in an angular change in the track angle of a predetermined amountsuch as, for example, 5 degrees, although any suitable value can beused. If step 930 detects that the actuation is long term (i.e.,continuous) or ongoing, a long term or continuous flight mode adjustmentis made at 942. In the example of a continuous actuation of left switch,SW1, the autopilot executes a continuous turn to the left. The turn ismaintained until step 944 detects that the actuation has ended. In anembodiment, continuous or long term turns executed by the autopilot canbe performed as standard rate turns for the given aircraft in which theautopilot is installed. For example, a standard rate turn for theRobinson R22 is 2 minutes for 360 degrees. Display 40 of FIG. 11 canrespond in any suitable manner such as, for example, by maintainingarrow 938 throughout the turn. Once the actuation ends, as detected at944, the turn ends and the current flight mode resumes on the new trackwith the method branching to normal operation 918.

Referring to FIG. 11, it should be appreciated that an incremental orcontinuous turn to the right can be performed in a manner that isconsistent with the descriptions above and with the presentation of anarrow on an opposing side of display 40 pointing to the right in theview of the figure. In the speed hold mode, actuations of fore switchSW3 and aft switch SW4 (FIGS. 1 and 2) can produce an acceleration ordeceleration to a new speed. For a momentary actuation, a suitableincremental change in the speed can be produced by step 934 of FIG. 9such as, for example, 5 knots, although any suitable incremental amountof change can be used. For a continuous actuation, the speed can becontinuously increased or decreased, for example, at a rate of 1 knotper second, by step 942 of FIG. 9. The current speed can then bemaintained as the current speed which is indicated at the end of theactuation. An active speed change can be indicated, by way ofnon-limiting example, using arrows 950 as seen in the screen shot ofFIG. 12 wherein upward pointing arrows represent a speed increase anddownward pointing arrows represent a speed decrease. A textualindication 952 such as, for example, ACCEL or DECEL can be provided withor without arrows 950. The presentation of these arrows and/or thetextual indication can be maintained, for example, for the duration ofthe actuation. It is noted that FIG. 12 illustrates an increase in speedfrom 56 knots to 61 knots as part of a continuous and ongoing increasein speed.

FIG. 13 is a screenshot of display 40 which illustrates an embodiment ofthe appearance of an embodiment of the display during the altitude holdmode at the time that the autopilot responds to the actuation of rightswitch SW2. The response to detection of the actuation can be an arrow954 pointing to the right. In the altitude hold mode, the autopilot canrespond to actuations of SW1 and SW2 in a manner that is essentiallyidentical to the responses described above in the speed hold mode. Ofcourse, an actuation of left switch SW1 can present arrow 938 of FIG.11, as opposed to arrow 954.

Turning to FIG. 14, another screenshot 40 illustrates an embodiment ofthe appearance of display 40 during the altitude hold mode responsive toan actuation of fore switch SW3. The detection of a momentary actuationof either SW3 or SW4 by method 800 can produce an incremental change inaltitude. By way of non-limiting example, the incremental change can be25 feet. In this regard, any suitable value can be used. Based on thedetection of a long term actuation of SW3 or SW4, the autopilot caninitiate a climb or descent, respectively, for the duration of theactuation. Upon detection of the absence of the actuation, method 800can return to normal operation in the altitude hold mode at the newaltitude. Responsive to the actuation of SW3, arrows 950 can appear onthe display which can be accompanied by a textual indication 958. Thearrows and/or textual indication can persist based on the duration ofthe actuation. The textual indication, in the present example, indicatesCLIMB or some other suitable term. In the instance of the actuation ofSW4, the textual indication can comprise DESCEND or some other suitableterm and arrows 950 can point downward in the view of the figure. It isnoted that FIG. 14 illustrates a climb from 1100 feet to 1125 feet aspart of a continuous and ongoing climb responsive to a long termactuation of SW3. In an embodiment, a continuous climb or descent can beperformed at a rate such as, for example, 500 feet per minute whichserves as a standard rate for the Robinson R22. In this regard, the ratecan be customized based on the given helicopter in which the autopilotis installed.

In view of the foregoing, it should be appreciated that the autopilot ofthe present application represents a significant advancement in terms ofsafety. For example, if a pilot were to inadvertently fly into a cloudand become disoriented, engagement of the autopilot will restore theaircraft to straight and level flight. Thereafter, the pilot can holdeither left button SW1 or right button SW2 to execute a turn, forexample, of 180 degrees and then fly forward out of the cloud in anappropriate flight mode.

The foregoing description of the invention has been presented forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form or formsdisclosed, and other modifications and variations may be possible inlight of the above teachings wherein those of skill in the art willrecognize certain modifications, permutations, additions andsub-combinations thereof.

What is claimed is:
 1. An autopilot system for selective control of anaircraft, the aircraft including a control stick operable to manuallycontrol the flight of the aircraft, said autopilot system comprising:one or more actuators in mechanical communication with the control stickof the aircraft; a pilot control interface including (i) an electricalresistance network that is selectively switchable between a plurality ofstates and (ii) a plurality of switches for pilot interaction therewithto selectively switch said electrical resistance network between saidstates such that each state exhibits an output resistance across anoutput interface that is made up of no more than two conductors; and anautopilot control unit mounted separate from said stick for electricallydriving the actuators based on the output resistance across the outputinterface and configured for automatic control of the aircraft in one ormore flight modes.
 2. The autopilot system of claim 1 wherein theelectrical resistance network is a parallel resistance network andincludes a null resistor having a finite value that is connected acrosssaid two conductors and said autopilot control unit is configured fordetection of a broken wire condition based on detecting a resistanceacross the two conductors that is greater than the finite value of thenull resistor and, responsive to detecting the broken wire condition, atleast issuing a notification to a pilot to take control of the aircraft.3. The autopilot system of claim 1 wherein an actuation of any one ofthe switches produces a resistance value across the two conductors thatfalls within a range of valid resistance values corresponding to saidstates and said autopilot control unit is configured for detectingresistance values across the two conductors that are above said range asbeing indicative of a broken wire condition and, responsive to detectingthe broken wire condition, at least issuing a notification to a pilot totake control of the aircraft.
 4. The autopilot system of claim 1 whereinthe electrical resistance network is a parallel resistance network andan actuation of any one of the switches produces a resistance valueacross the two conductors that falls within a range of valid resistancevalues corresponding to said states and said autopilot controller isconfigured for detecting resistance values across the two conductorsthat are below said range as being indicative of a shorted conditionand, responsive to detecting the shorted condition, at least issuing anotification to a pilot to take control of the aircraft.
 5. The pilotcontrol interface of claim 1 further comprising: an engage/disengageselector that includes first and second resistors forming part of theelectrical resistance network and first and second switches associatedwith the first and second resistors, respectively, such that a pilotactuation of the engage/disengage selector, during normal operation,changes a state of the first and second switches to electrically connectthe first and second resistors to said two conductors to present anengage/disengage resistance across the two conductors.